The use of certain heavy metals, especially copper and copper alloys in antifouling coatings for ships and other marine structures is well known.
The use of gelcoats based on unsaturated polyester resins for GRP marine structures such as boats is also well known. However it is also well known that copper and its compounds are efficient inhibitors for unsaturated polyester resins, the effect first having been noticed when attempts were made to embed electrical windings in polyesters, and also having been noticed when GRP tubes were wound on brass mandrels and their inner surface was found to be discoloured and undercured.
This inhibiting effect was put to practical use by the use of small quantities (0.25-10 ppm Cu) of oil-soluble copper salts, such as the naphthenate, to improve the storage stability of liquid unsaturated polyester resins (G.B. Pat. No. 834,286).
Attempts to overcome the problem of preventing inhibition of cure in the presence of copper are illustrated by G.B. Pat. No. 967,921 which covers the addition of oxalic acid, by the use of hydroxy polycarboxylic acids such as tartaric acid to prevent inhibition in contact with copper (U.S. Pat. No. 2,566,739), and by G.B. Pat. No. 1,526,597 which covers the addition of benzotriazole to the resin to get a good bond between copper foil and glass-reinforced polyester in the manufacture of copper clad laminates for electrical purposes.